Discover how to write effective multi-threaded code in Java; learn why problems can occur with Java multithreading and how to fix those problems.
In this tutorial we'll look at the two main ways to start a thread in Java. If you want to start lots of threads all at once you'll want to use thread pools, which we'll look at in a future tutorial; the methods in this tutorial are most suitable for starting one or a small number of threads. In case you're going for a job interview or taking an exam, this is a classic interview/exam question!
This video looks at basic thread communication in Java using boolean flags with the volatile keyword. I also take a look at why volatile isn't good enough for most situations.
The basics of using the synchronized keyword in Java to stop threads messing up each other's work. What's an intrinsic lock, and why do we need it?
How to speed up your multithreaded code by locking only those sections of code that you need to, rather than using synchronized methods and locking your whole object. Don't forget to maximize to fullscreen so you can see the code. You can also find the code on caveofprogramming.com.
How to use thread pools to manage lots of threads to complete lots of similar tasks. Source code available on caveofprogramming.com
How to use the fantastic CountDownLatch class in Java to simplify your multithreaded code.
A tutorial on how to implement the producer-consumer pattern in Java using the ArrayBlockingQueue Java class. Producer-Consumer is the situation where one or more threads are producing data items and adding them to a shared data store of some kind while one or more other threads process those items, removing them from the data store.
A tutorial on wait and notify; low-level thread synchronization methods in Java that allow you to avoid having vile process-consuming polling loops in your code. Code on caveofprogramming.com. Wait and notify allow you to have sleeping threads that are woken up by other threads. "Why, exactly what I've been looking for!" I hear you say. Yes, even people who don't program in Java can enjoy using these fantastic methods. OK, maybe that's going a bit far.
A tutorial on how to implement the producer-consumer pattern in Java using the "low level" keywords wait, notify and synchronize. (See tutorial 7 for the high level version). Code on www.caveofprogramming.com
How to use the ReentrantLock class in Java as an alternative to synchronized code blocks. ReentrantLocks let you do all the stuff that you can do with synchronized, wait and notify, plus some more stuff besides that may come in handy from time to time.
The causes of deadlock and two things you can do about it. This video also covers how to write a method that can safely acquire any number of locks in any order without causing deadlock, using the tryLock() method of ReentrantLock.
After working as a software developer and contractor for over 14 years for a whole bunch of companies including CSC, Proquest, SPSS and AT&T in the UK and Netherlands, I decided to work full-time as a private software trainer. I now live in the beautiful city of Budapest, Hungary, from where I run the website Cave of Programming.